1. Field of the Invention
The present invention relates generally to equipment used in semiconductor processing. More particularly, the present invention relates to a multi-element mirror assembly suitable for use in an extreme ultraviolet lithography (EUV) system.
2. Description of the Related Art
Extreme ultraviolet (EUV) lithography is a semiconductor fabrication technology which enables semiconductors with small features, e.g., features with dimensions of approximately 45 nanometers (nm) or less, to be produced. In EUV lithography, a laser may heat xenon gas to create a plasma, although there are other methods used to make EUV plasmas. Electrons come off the plasma and radiate light.
FIG. 1 is a block diagram representation of an EUV lithography system. An EUV lithography system 100 includes a vacuum chamber 128 which contains a source 104. Source 104 provides electrons that radiate light, and includes a plasma source 108 and a collector mirror 112 that reflects electrons which come off of the plasma generated by plasma source 108 into an illuminator unit 116b of a body 116 of EUV lithography system 100. Illuminator unit 116b is a condenser that effectively collects light and directs or otherwise focuses the light onto a reticle 120. That is, illuminator unit 116b conditions light from plasma source 108 to improve uniformity. The light reflects off of reticle 120, through projection optics 116a of body 116, and onto a surface of a wafer 124.
Mirrors included in an EUV lithography system generally absorb some of light or radiation that comes into contact with the mirrors. Such mirrors (not shown) may be associated with illuminator unit 116b as well as with projection optics 116a. A mirror may effectively be a mirror assembly that includes a plurality of mirror blocks that are substantially directly cooled by a heat exchanger that includes wells of liquid metal, as described in co-pending U.S. patent application Ser. No. 12/261,798, filed Oct. 30, 2008, which is incorporated herein by reference in its entirety. As shown in FIG. 2, a mirror assembly may include a base plate and multiple mirror blocks. A mirror assembly 240 includes a plurality of mirror blocks 240a. Each mirror block 240a is coupled to a shared base plate 240b. 
To align mirror blocks 240a relative to base plate 240b, press-fit pins are generally used. Press-fit pins are may be included in base plate 240b, and holes and slots into which the press-fit pins are positioned may be included in mirror blocks 240a. While the use of press-fit pins is effective in accurately aligning mirror blocks 240a, there may be insufficient space in mirror assembly 240 to accommodate press-fit pins, holes, and slots. For example, when mirror blocks 240a include multiple mirror facets, there is typically insufficient space for press-fit pins, holes, and slots. In addition, liquid metal wells (not shown) and/or posts (not shown), e.g., for transferring heat, included in mirror assembly 240 may occupy any additional space available in mirror assembly 240.